This invention concerns an auxiliary chain for drawing assemblies in drawing machines.
The drawing assemblies to which the chain according to the invention is applied are of the type comprising two opposite and counter-rotating tracks which collaborate with a product being processed to draw it through a die plate of a drawing machine.
The auxiliary chain according to the invention is suitable to be arranged inside a respective track to reduce the friction between the latter and relative rigid supporting means, and to distribute uniformly the forces of thrust which act thereon during the drawing steps.
During the operating cycles, very high loads-may affect the tracks according to the reduction in section to be imparted to the products being worked.
The state of the art includes drawing assemblies used in drawing machines and consisting of two counter-rotating tracks opposite each other with respect to the drawing axis, each comprising a plurality of links on each of which respective pads are mounted, suitable to grip and draw the metal product being worked through a draw plate.
Motion is supplied to every track by a pair of toothed wheels, normally a drive wheel and a driven wheel, which are mounted at the ends of a rigid supporting plate around which the track itself is closed in a ring.
In the state of the art, between the supporting plate and the relative track, an auxiliary chain is provided, wound around the supporting plate, on which the links of the track rest at least in the rectilinear segment of the latter.
These auxiliary chains are used to reduce the friction between the tracks and the relative supporting plate, and to discharge uniformly the high forces of thrust which act on the individual links of the tracks, particularly during the operational drawing cycles.
In the state of the art, the auxiliary chain is made up of links, and every individual link consists of a containing cage inside which two or more idler rolls are housed.
Each link also comprises first pins suitable to associate the different containing cages together, creating the structural connection of the chain, and second pins suitable to associate the individual idler rolls to the relative containing cages.
The pins, and particularly the first pins suitable to associate the individual links of the auxiliary chain, are subjected to considerable mechanical stresses since a large proportion of the thrust forces of drawing and compression discharged onto the idler rolls by the tracks of the drawing assembly are in fact discharged onto said pins.
The pins of conventional auxiliary chains, therefore, are easily subject to breakages, and when these happen, the machine necessarily has to be stopped for a long time.
Another disadvantage of conventional auxiliary chains is that the cages containing the idler rolls are difficult to achieve and assemble, particularly due to the presence of at least three pins for every link.
Furthermore, conventional auxiliary chains are not very flexible because each link comprises at least two idler rolls and therefore do not adapt very well to the profile of the supporting plate, particularly in the curved segments of the latter.
The present Applicant has devised and embodied this invention to overcome the shortcomings of conventional auxiliary chains and to obtain further advantages as shown hereafter.
The main purpose of the invention is to achieve an auxiliary chain for drawing assemblies in drawing machines which will be easy to achieve and assemble, efficient, resistant, unlikely to break or malfunction and suitable to bear very high loads.
Another purpose of the invention is to achieve an auxiliary chain suitable to adapt in the best possible way to the curves defined by the profile of the rigid supporting plate on which it is wound.
Another purpose of the invention is to achieve an auxiliary chain consisting of a limited number of components and wherein the same pin is used both to support an idler roll and also to couple two adjacent links together.
Another purpose is to achieve an auxiliary chain wherein the forces of thrust acting on the idler rolls are discharged uniformly over the entire link, thus reducing the risks of breakages.
In accordance with these purposes, an auxiliary chain according to the invention consists of a plurality of links, each comprising an idler roll, a join pin and two connection elements arranged opposite each other respectively on one side and the other of the link, each of which is suitable to cooperate with a respective end of the idler roll.
Each connection element is suitable to be arranged at least partly superimposed with respect to at least two adjacent idler rolls of the chain.
Each connection element is equipped with two through holes, respectively first and second, and each idler roll is equipped with an axial hole into which the relative pin is inserted.
In the auxiliary chain according to the invention, on both sides thereof, two of the adjacent connection elements are suitable to be partly superimposed one on top of the other in such a manner that the first hole of each connection element is suitable to align with the second hole of the adjacent connection element and also with the axial hole of an idler roll.
In the three holes thus aligned, the respective join pin is then inserted and left free to rotate but constrained at its ends at least to the more outward of the two, superimposed connection elements.
In the preferential embodiment of the invention, the join pin is inserted with a gap inside the axial hole of the relative idler roll, so that the thrust forces and the stresses transmitted by the tracks to the idler rolls do not affect the relative pins.
According to a variant, an element of association and constraint, such as, for example, a bushing or similar, is inserted into the first and second aligned holes of two adjacent and partly superimposed connection elements. According to one characteristic of the invention, the thrust forces transmitted by the tracks to the idler rolls are discharged prevalently onto the connection elements in correspondence with the zones of frontal and/or lateral contact between the latter and the idler rolls themselves. These contact zones are studied to discharge the forces acting on the idler rolls in a uniform and well-distributed manner, and absorb most of the stresses so as to preserve the join pins and thus increase the working life of the auxiliary chain.
In the preferential embodiment of the invention, the contact zones coincide substantially with the annular portions provided in correspondence with the two ends of every idler roll.